Hydraulic performance of drip irrigation system with branch and lateral pipes installed jet-pulse tee

Drip irrigation has the problems of easy blockage and low irrigation uniformity under low head (less than 10 m). Pulse drip irrigation technology can generate periodic and turbulent pulsed flow, which is beneficial to improve the anti-blockage ability and irrigation uniformity of the emitter. In order to analyze the influence of pulsed flow on the hydraulic performance of drip irrigation system, a branch jet-pulse tee was designed based on the principle of wall attachment and switching of jet, and a combined test with lateral jet-pulse tee was carried out. A total 4 irrigation districts were constructed according to different combinations, of which the branch and lateral pipe tees of No. I irrigation district were both jet-pulse tees; in No.II irrigation district, the branch pipe was jet-pulse tee and the lateral pipe was ordinary jet tee; in No. III irrigation district, the branch pipe was ordinary jet tee and the lateral pipe was jet-pulse tee; and the branch and lateral pipe tees of No. IV irrigation district were both ordinary jet tees. In irrigation district, the length of lateral pipe was 60 m, and the inlet head of branch tee was set to 9.5, 12, 14 and 15.5 m, respectively. Turbine flowmeter was installed at branch pipe tee outlet and lateral pipe tee inlet to record branch pipe tee outlet flow rate and lateral pipe tee inlet flow rate, respectively. The flow rate was the difference between the initial value and the final value in the flowmeter test. The high-speed camera captured the oscillation of pressure gauge pointer of lateral jet-pulse tee outlet to record pulse frequency and maximum pressure. Head loss was the difference between the inlet pressure of branch tee and the maximum outlet pressure of lateral pipe tee. The results showed that the total flow rate of No. I irrigation district was the smallest and the dripper flow rate was less than the rated value (2.7 L/h) because the No. I irrigation district with jet-pulse tees installed in both branch and lateral pipes had intermittent pulsed flow. The pressure and flow rate at the outlet of branch tee followed power function relationships with the fitting degree higher than 0.96 and the root mean square error smaller than 28 L/h. The irrigation uniformity coefficient of irrigation system in No. I irrigation districts ranged from 95.88% to 98.56%, which was higher than the other 3 irrigation districts by 1.02%-4.43% respectively. The flow deviation rate ranged from 8.35% to 15.14% in No. I irrigation districts, which was lower than the others by 0.46%-5.72%. It proves that the irrigation uniformity of No. I irrigation districts is the best. In No. I, II and III irrigation districts, the pulse frequency of branch and lateral pipe jets increased with the increase of the inlet head. Head loss from branch tee inlet to lateral pipe tee outlet in No. I irrigation district was 0.9-1.6 m under different branch pipe tee inlet heads, which was not significantly different from the other systems. The results of this study will contribute to the selection of the optimal combination mode of branch pipe tee and lateral pipe tee in irrigation district, and provide valuable information for the research, development and application of jet technology in pulsed drip irrigation system. In the future research, it is necessary to test the loss along the lateral pipe, observe the distribution of pressure, flow rate and pulse performance in the lateral pipe, and further evaluate the uniformity and anti-clogging ability of irrigation. © 2019, Editorial Department of the Transactions of the Chinese Society of Agricultural Engineering. All right reserved.